Holographic, diffractive, and 3D structured images have been used in conjunction with printing applications to capture the visual attention of the viewer by producing enhanced visual effects via light refraction depending on the viewing angle. Holographic images can also provide different viewing effects such as flip or 3-dimensional images. Today, however, the marketplace demands more sophisticated integration between structured images and associated conventional printing. Although registration of random structured images to printing requires only controls between the tooling and the printing, registration of non-random structured images to printing requires precise control between the tooling, the structured images and the printing. This is a particularly difficult challenge when the non-random images are applied to a substrate made up of a series of individual sheets (a “sheeted substrate”). For example, while non-random holographic designs are often used as a higher level security feature to produce printed matter with registration between meaningful structured images and printing on continuous webs, producing such product in a sheeted substrate currently is costly and difficult.
Conventional processes for applying structured images onto resin/film substrates are subject to substrate distortion due to the substantial heat required to emboss the image into the film. Also, current systems for producing printing in registration with diffractive or holographic images on a laminated sheeted substrate often encounter problems such as displayed shim lines and missed registration. These problems may be caused by sheeting after lamination, by holographic material distortion, or by various tensions produced in the holographic material when it is made by conventional processes.
Systems for laying down holographic and other embossed images into a layer of liquid resin by using a master film or master cylinder and then curing are also known. However, this approach has been used only for embossing holographic images with random designs into the uncured resin on the sheet or web substrate and not where registration between the printing and non-random holographic images on the master web is required.
Casting and registering a holographic image by heat embossing holographic flexible film to a pre-printed sheeted substrate also produces misalignment between the printing on the substrate sheet and the cast holographic images from the master web due to inconsistent spacing between registration marks. Furthermore, inconsistent spacing during sheeted substrate transport also occurs after the substrate sheet was registered coated which amplifies the difficulty of registration between the printing and the non-random holographic images.
While these problems are exacerbated when the system is run at high speed, they sometimes can be resolved by casting multiple times with a different master web combined with spot application. However, multiple casting with a different master web in selected areas will produce reduced rub resistance in non-casting areas if more than one random design is chosen for casting at the selected area. In addition, there will be discernable differences in gloss on the printed layer between cast and non-cast areas. Such gloss and rub resistance concerns arise, for example, in sheet material produced in accordance with the system of U.S. Pat. No. 5,003,915.
My U.S. patent application Ser. No. 12/125,631 entitled “Method for Transferring Holographic and Other Microstructure or Refractive Images Onto a Web-Carried Resin Coating in Registration with Printing on the Web” filed May 22, 2008 describes, inter alia, apparatus and methods for producing holographic images on a continuous shrink film web through a master web application. However, this patent application focuses on registration between the master film and the web substrate by stretching the shrink film web to match the repeat length of the images on the master web. So, the repeat length of the master web must be shorter than the repeat length of each printed image on the shrink film web. In contrast, the present sheeted substrate system calls for different (and unique) approaches to address the spacing between the individual sheets of the sheeted substrate.
U.S. Pat. Nos. 4,933,120; 5,003,915; and 6,775,036 describe apparatus and methods for producing holographic patterns by using a master cylinder or master film to apply an embossed image against a coated substrate web. However, apparatus described in these patents are severely limited as to substrate thickness and registration between printed images on the web substrate and the images on the master cylinder. This is because, inter alia, the dancer roll mechanism used cannot compensate for the accumulating difference in image spacing on the substrate due to web distortion caused by tension, moisture and temperature changes. In addition, the dancer roll can only be used on web substrates and not with sheet substrates as described in the current invention. Finally, U.S. Pat. Nos. 4,933,120 and 5,003,915 transfer liquid resin from a relief mold.
Therefore, if a system were available that could achieve accurate registration of structured images on a sheeted substrate at high speed that could accommodate different images, that eliminated seam lines, and that eliminated the difference in gloss and rub resistance, particularly significant contributions to the art would be at hand.